The following is an explanation of a conventional semi-conductor circuit apparatus, for example, a conventional inverter apparatus, which is wired to a conventional printed circuit board.
FIG. 9 is a basic circuit diagram of a conventional inverter apparatus. In FIG. 9, three-phase current alternating at a power-frequency, which is inputted through power terminals 54, is converted into direct current by a diode module 51. The converted direct current is smoothed by a smoothing capacitor 53, and inputted into a transistor module 52. The transistor module 52 invents the direct current to three-phase alternating current having a desired frequency. The inverted alternating current is output from load terminals 55. The transistor module 52 is controlled by a control device 56. The above-mentioned inverter apparatus provides a resistor 57 for limiting a current surge in order to control the current surge when the inverter apparatus starts to operate. If the resistor 57 for limiting the current surge continues to operate during operation of the inverter apparatus, a voltage drop caused by the resistor 57 is generated in the inverter apparatus. For solving the above-mentioned problem, the resistor 57 is connected in the inverter apparatus only at the starting time of the inverter apparatus. Thereafter, an electromagnetic contactor 58, which creates a short circuit between the input terminal and output terminal of the resistor 57, shorts the resistor 57 during the operating time of the inverter apparatus except at the starting time.
Such an inverter circuit of an inverter apparatus, which is connected by a printed circuit board, is disclosed in Japanese published unexamined utility model application No. Sho 60-83292 (Jikkai Sho 60-83292) as a semi-conductor circuit apparatus. FIG. 10 is a cross sectional side view showing the structure of the semi-conductor circuit apparatus. In FIG. 10, parts and components to which correspond like elements shown in FIG. 9 are shown by the same numerals. As shown in FIG. 10, main circuit devices, such as the diode module 51, the transistor module 52 and the smoothing capacitor 53 are located inside a base 59. The above-mentioned main circuit devices located in the base 59 are covered by a cover 65. Radiating fins 60 are provided on the bottom face of the base 59 to cool the main circuit device due to the current flowing therein. The main circuit devices are electrically connected to one another by a main circuit printed board 66. Connecting terminals 51a, 52a, 53a of the main circuit devices are fixed to the main circuit printed board 66 by bolts 51b, 52b, 53b, respectively.
As shown in FIG. 10, a control device 56 for controlling the transistor module 52 is mounted on a control circuit printed board 70 which is electrically and mechanically connected to the main circuit printed board 66 by connectors 69.
In the above-mentioned semi-conductor circuit apparatus, each insulation distance between the connecting terminals 51a, 52a, 53a, 53a of the main circuit device is formed along the surface of the main circuit printed board 66 by an insulation sheet made of a laminate plate.
If floating dust or suspended particulate stick on the main circuit printed board 66 and accumulate, the insulation along the surface of the main circuit printed board 66 deteriorates. In view of the deterioration of the main circuit printed board 66, the distance between the connecting terminals of the main circuit devices in the conventional semi-conductor circuit apparatus should be increased to insulate the area between the connecting terminals 51a, 52a, 53a, 53a. As a result, the conventional semi-conductor circuit apparatus is large in size.
As shown in FIG. 10, since there is an aperture A between a top face of the main circuit devices and a bottom face of main circuit printed board 66, the floating dust or suspended particulate are likely to collect in the aperture A. As a result, insulation deterioration occurs in the aperture A between the connecting terminals for three-phase or the connecting terminals and main circuit printed board 66.
In order to solve the above-mentioned problem, a "printed circuit board" shown in FIG. 11 is disclosed in the Japanese published unexamined utility model application No. 59-189257 (Jikkai Sho 59-189257). FIG. 11 is a cross sectional view showing a printed circuit board 508 on which a relay 505 is mounted. Connecting terminals 506, 507 of the relay 505 are inserted into holes 512, 513 of the printed circuit board 508 be in electrical connection with copper foils 509, 510. The copper foils 509, 510 are conductor foil which is printed on the printed circuit board 508. The printed circuit board 508 provides a lib-shaped projection 511 between two holes 512 and 513 to isolate two copper foils 509 and 510. In other words, a distance for insulation, namely creepage distance, between the connecting terminals 506, 507 increases by providing the projection 511 made of an insulation material.
However, the above-mentioned printed circuit board 508 cannot be manufactured by a normal etching step or drilling step of a copper-clad laminate board generally utilized for manufacturing a typical printed circuit board having a flat surface. Therefore the printed circuit board 508 has to be manufactured by a special manufacturing process for printing the circuit on the insulation board. As a result, using such a printed circuit board increases the manufacturing cost of the apparatus.